The U.S. Department of Justice has thrown its weight behind the nation’s largest TV broadcasters in their upcoming Supreme Courtshowdown against upstart online video service Aereo. In a brief filed with the high court on Monday, the feds said that Aereo is “clearly infringing” on the copyrights of the major broadcasters by picking up their free, over-the-air TV signals and streaming them over the Internet.

Aereo, which launched in February 2012, uses thousands of dime-sized antennas to pick up TV broadcast signals, which it sends to its customers over the Internet for a monthly fee starting at $8. The startup has angered the major broadcasters, including NBC, FOX, ABC and CBS, which argue that the service is illegal because it doesn’t pay to pick up the signals it streams to users.

Aereo “transmits copyrighted broadcast programs to the public, without the authorization of the copyright holders, and is therefore liable for infringement,” the Justice Department said in its 34-page brief. The U.S. show of support for the broadcasters, which was authored by the Solicitor General, amounts to a significant setback for Aereo, which is trying to convince the Supreme Court that its streams constitute legally protected “private performances,” not copyright protected “public performances.”

The National Association of Broadcasters, an industry trade group, praised the government’s support for the networks. “NAB is pleased that the Solicitor General — who represents the U.S. Government before the Supreme Court — agrees with broadcasters that Aereo is violating copyright law,” NAB Executive Vice President of Communications Dennis Wharton said in a statement. “We look forward to oral arguments and a final decision in the case, and we’re hopeful that Aereo will be declared a copyright infringer.”

In an interview with TIME on Sunday, Aereo CEO Chet Kanojia warned that if Aereo loses, there could be significant consequences for the cloud storage industry, including remote, or network, DVR services. “If Aereo is not allowed to continue, neither are network DVRs, which would be a huge step backwards for a lot of these industries,” Kanojia said.

But the Justice Department poured cold water on that notion. “A decision rejecting [Aereo’s] infringing business model and reversing the judgment below need not call into question the legitimacy of innovative technologies that allow consumers to use the Internet to store, hear, and view their own lawfully acquired copies of copyrighted works,” the government said in its brief.

The broadcasters argue that Aereo’s service amounts to blatant theft because the company doesn’t pay “retransmission fees,” unlike cable and satellite providers, which pay billions of dollars for the right to offer popular TV programming to their subscribers. The broadcasters have warned that if Aereo prevails, they could take their primetime shows off free TV and move them to pay channels like Showtime.

Last year, federal courts in New York and Boston agreed with Aereo’s position that it is transmitting legally protected “private performances” to individuals over their own leased antennas. But last month, a federal judge in Utah ruled in favor of the broadcasters, increasing the urgency for a Supreme Court resolution.